Chapter 48, Problem 1Q

Summary Introduction

To analyze:

The variations in Po₂ (in units of mmHg) in a typical open-close-fluttering cycle. Also explain the estimated mm Hg Po₂ in the atmosphere and inside the tubes of trachea in all the three given experiments shown in figure B. Here, 1 kPa (kilopascal) = 7.5 mm Hg.

Given information:

The microscopic plastic tubes were inserted into the tracheae of the pupae of Attacus atlas moths by the researchers to study the tracheal function in the moths. The microtubes were attached to the sensors for recording the rate of CO₂ that was released from the tracheae and also the intratracheal concentrations of O₂.

The pupae were placed in the chambers by the researchers and the normal atmospheric levels of the gases were maintained. Researchers then recorded the behavior of spiracles, rate of CO₂ release, and O₂ concentrations in the tracheae. The results are shown in figure A.

In order to examine the spiracles performance in the different atmospheric conditions and their effects on the rate of CO₂ release and O₂ concentrations, pupae were exposed to the different levels of atmospheric O₂. The levels of the release of CO₂ and O₂ concentrations were calculated during the fluttering stage as shown in the figure B.

Introduction:

The insectys have a unique mechanism of air exchange in their bodies. The respiratory system of the insects consists of the tracheae that is responsible for the gaseous exchange in and out of tissues. There are spiracles present that guards the trachea. They are valve-like and either remains open, closed, or in a fluttering state.

Explanation of Solution

Intratracheal partial pressure of O₂ during the open phase of the spiracles in the tracheae as shown in the figure is 20.4 kPa.

If 1 kPa = 7.5mm Hg, then, Po₂ during the open phase will be,7.5*20.4 = 153 mm Hg.

During the closed phase, Po₂ decreases to 4–5 kPa.

If 1 kPa = 7.5mm Hg, then, P_O2 during the closed phase will be,7.5*5 = 37.5 mm Hg.

During the fluttering phase, if the oxygen concentration is changed as shown in figure B, the P_O2 will be calculated as

Case1, If 1 kPa = 7.5mm Hg, 7.5*6.4 = 48 mm Hg.

Case2, If 1 kPa = 7.5mm Hg, 7.5*21.2 = 159 mm Hg.

Case3, If 1 kPa = 7.5mm Hg, 7.5*40.2 = 301.5 mm Hg.

Conclusion

Thus, it can be concluded that the changes in approximate mm Hg of PO₂ in a typical open-close fluttering cycle are 153 mm Hg and 7.5 mm Hg during the open and closed phases, respectively. Also, in the tubes of the trachea, in all the three given cases, the pressure was 48 mm Hg, 159 mm Hg, and 301.5 mm Hg, respectively.